This section provides background information related to the present disclosure which is not necessarily prior art.
Recently, there has been renewed interest in the use of turbocharging in internal combustion engines. As is well known, turbochargers are useful in providing compressed air in to the induction system of the engine to provide increased engine performance relative to normally aspirated engines. In fact, it has been found that in many applications use of a turbocharging system can permit sufficient increased performance to enable smaller engines to be used therein. As a result, overall fuel efficiency of the vehicle can be substantially improved.
Generally, normally aspirated engines pull or otherwise suck air into the combustion chamber in response to the mechanical downward intake stroke of the piston. In this way, atmospheric pressure is used to drive air into the combustion chamber via the intake valve in response to the downward intake stroke of the piston. However, turbochargers can be used to increase the pressure of this air upstream of the intake valve to permit a higher density of air to be forced, or drawn, into the combustion chamber. This increased air density can be mixed with increased fuel, thereby converting more fuel energy into usable power.
Turbochargers generally include a compressor for drawing in ambient air and compressing it as it enters the intake manifold. This results in a greater mass of air entering the cylinders on each intake stroke. The compressor of the turbocharger is mechanically spun in response to a turbine or scroll. The scroll is disposed within the exhaust stream and thus turns in response to the kinetic energy of the engine's exhaust gases.
It should be understood that typical exhaust streams of internal combustion engines are not constant. That is, as the engine operates and each of the individual cylinders operates through their combustion cycles, burned exhaust gases are released during an upward exhaust stroke of the piston. During this exhaust stroke, a plug or pulse of exhaust gases is forced out of the combustion chamber and into the exhaust system of the engine. This plug of exhaust gases flows along the exhaust system to the turbocharger and impacts the scroll of the turbocharger, thereby rotatably driving the scroll and the associated compressor. However, in some applications, these plugs or pulses can overlap in such a way as to reduce the effective flow of the exhaust stream, thereby reducing the available kinetic energy available to drive the turbocharger. This is particularly evident in engines having few cylinders as each pulse is more readily discernible.
In these applications, a dual scroll or twin scroll turbocharger can be used in which separated exhaust manifolds from selected cylinders are routed to one of two exhaust inlets of a single turbocharger. This technique of separating the exhaust streams can permit efficient use of the kinetic energy of the exhaust streams and can vastly improve the low end performance of the turbocharger and enhance the transient response of the engine.
However, turbocharging systems and the associated exhaust system operate at extremely high temperatures. For example, in some applications, the exhaust gases existing the combustion chamber and traveling to the inlet of the turbocharger can reach 950° C. or higher. These temperatures are often greatest when the engine is operated at its ideal stoichiometric mixture—that is, at the air to fuel ratio that permits generally all fuel to be oxidized without excess air.
Therefore, there exists a need in the relevant art to provide an integrated exhaust manifold capable of providing split exhaust routing to a dual scroll turbocharger. Moreover, there exists a need in the relevant art to provide a cooling system for use with an integrated exhaust manifold to maintain proper temperatures for equipment protection. Furthermore, there exists a need in the relevant art to provide a cooling system for use with an integrated exhaust manifold capable of permitting stoichiometric operation across the entire speed and load maps of the engine.